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Collectors are the workhorses of Stream terminal aggregation in Java 8. They let you join strings, group and partition data, build specific collection types, and compute statistics — all in a fluent, readable style. 1) Collectors.joining() — Concatenate elements Concatenate stream elements into a single string with optional delimiter, prefix, and suffix. List<String> words = Arrays.asList("apple", "banana", "cherry"); String joined = words.stream() .collect(Collectors.joining(", ", "[", "]")); System.out.println(joined); // [apple, banana, cherry] 2) Collectors.groupingBy() — Group by classifier Group elements based on a key extractor. Default downstream is toList() . List<Person> people = Arrays.asList( new Person("John", "New York"), new Person("Wick", "London"), new Person("Smith", "New York") ); Map...

In our previous post, we explored intermediate operations in Java Streams. Now, let’s move to terminal operations . These are the final operations that produce a result (like a value, collection, or side-effect) and terminate the stream pipeline. 1. forEach() The forEach() method is used to perform an action for each element of the stream. List<String> words = Arrays.asList("apple", "banana", "cherry"); words.forEach(word -> System.out.println("item is " + word)); 2. collect() The collect() method gathers the elements of a stream into a collection (like a List, Set, or Map). List<Integer> nums = Arrays.asList(1,1,2,2,2,3,4,5,5,5,6); Set<Integer> res = nums.stream().collect(Collectors.toSet()); System.out.println(res); 3. reduce() The reduce() method performs a reduction on the elements of the stream using an accumulation function. List<Integer> nums = Arrays.asList(1,2,3,4,5); Optional<Integer...